From the viewpoint that a cBN sintered material has high hardness and high thermal conductivity second only to diamond and further has low affinity with iron based material, the cBN sintered material is preferably used as a cutting tool of an iron based work material such as steel or cast iron, conventionally.
In order to improve the performance as a cutting tool, several proposals have been made to further improve the strength, toughness, hardness, and the like of the cBN sintered material.
For example, in Japanese Unexamined Patent Application, First Publication No. H8-197307, in preparing the cBN sintered material by ultra-high pressure sintering, it is proposed to improve the strength and toughness of the cBN sintered material by making the binder phase into a skeleton structure and making a structure in which cBN particles as hard particles, and a reaction product formed of: a boride and a nitride of Al; and a boride of Ti are dispersed in the binder phase structure.
In addition, in Japanese Patent Publication No. 5032318, in the cBN sintered material, in order to remove oxygen adsorbed on the surface of cBN particles when cBN particles are bound, it is proposed to achieve compatibility between improvement in heat resistance and improvement in toughness of the cBN sintered material by using Ti or Al as a raw material to act as a getter of oxygen to prevent alteration of the cBN particles themselves caused by the solid solution of oxygen into the cBN particles, and to form a structure having a continuous structure in which the cBN particles are bound to each other and in which the binder phases are bound to each other.